1. Field of the Invention
The present invention relates in general to automatic document feeders for facsimile machines and, more particularly, to an improved structure in such document feeders for reliably feeding at least 30 sheets of documents into a facsimile machine one by one without misfeeding.
2. Description of the Prior Art
With reference to FIG. 1, there is shown in a schematic view a typical facsimile machine in a data transmitting operation. In the data transmitting operation, a plurality of documents 1 printed with the data are laid on a document plate 2 of the facsimile machine. When operating the facsimile machine in this state, the lowest document 1 is first fed into the facsimile machine by rotation of an automatic document feeding (ADF) roller 3 cooperating with the frictional force of an ADF rubber 4. The lowest document fed into the facsimile machine is in turn nipped by a pair of feeding rollers 5 and runs in the facsimile machine with a predetermined interval between it and a later document.
In the above typical facsimile machine, the contact angle between the ADF roller 3 and the ADF rubber 4 is limited to a predetermined angle so that it requires additionally use of a document feeder or a device for feeding the documents 1 to the nip between the ADF roller 3 and the ADF rubber 4 of the facsimile machine one by one when data printed on at least 30 sheets of documents 1 are to be transmitted by the facsimile machine.
In the prior art, the document feeder for feeding at least 30 sheets of documents 1 to the nip between the ADF roller 3 and the ADF rubber 4 of the facsimile machine comprises a cam roller facing the ADF roller 3 and a drive motor for driving the cam roller. The drive motor drives the cam roller only when the documents 1 need feeding, thus to feed the documents to the nip between the ADF roller 3 and the ADF rubber 4 one by one in such a manner that the lowest document is first fed. However, with the additional cam roller and the cam roller drive motor, the above document feeder is increased in its production cost.
In order to combat this problem, there has been proposed another type of document feeder is which the cam roller is rotated by the rotational force of the ADF roller 3 as shown in FIG. 2. This document feeder comprises a drive gear 6 rotated by an outside drive force, a driven gear 8 gearing into the drive gear 6 and a first shaft 7 integrally coupled to the driven gear 8. The ADF roller 3 is fixed to a second shaft 9, which shaft 9 is placed such that it is close to the first shaft 7. A spring 10 is fitted over both the first and second shafts 7 and 9 and functions as an one way clutch. The document feeder further includes a third shaft 11, which is parallel with the second shaft 9, and a timing belt 12 wrapped about the second and third shafts 9 and 11 for making these shafts 9 and 11 cooperating with each other. A pair of cam rollers 13 is fixed to the third shaft 11.
In operation of the above document feeder of FIG. 2, the drive gear 6 is rotated by the outside drive force or the rotational force of an additional drive motor (not shown) so that the driven gear 8 gearing into the drive gear 6 is rotated. The rotational motion of the driven gear causes the first shaft 7 to be rotated. The rotational motions of both the driven gear 8 and the first shaft 7 cause the spring 10 fitted over the first and second shafts 7 and 9 to be tightened due to the frictional force of the outer surfaces of the first and second shafts 7 and 9. The first and second shafts 7 and 9 are thus integrated into a single body and, as a result, the rotational force of the drive gear 6 is transmitted to the second shaft 9 through the first shaft 7. Here, the tightening of the spring 10 because of both the rotational motion of the drive gear 6 and the frictional force of the first shaft 7 is caused by the fact that there is provided a narrow gap of about 0.05-0.1 mm between the first and second shafts 7 and 9 and the spring 10.
When the ADF roller 3 is rotated by the rotational force of the second shaft 9, the lowest document 1 which has been nipped between the ADF roller 3 and the ADF rubber 4 is fed into the facsimile machine owing to the rotating frictional force of the ADF roller 3. When there is no document between the ADF roller 3 and the ADF rubber 4, the lowest document laid on the document plate is fed into the nip between the ADF roller 3 and the ADF rubber 4 owing to the rotational motion of the cam roller 13. Of course, the cam roller 13 is rotated by the rotational motion of the third shaft 11, which shaft 11 is applied with the rotational force from the second shaft 9 through the timing belt 12.
It has been noted that the above document feeder has an advantage in that it uses only one motor when it feeds at least 30 sheets of documents into the facsimile machine one by one by rotating the cam roller 13.
However, the above document feeder also has a disadvantage in that the cam roller 13 is mounted on the third shaft 11 which should cooperate with the second shaft 9 in addition to the timing belt 12. With the third shaft 11 and the timing belt 12, the above document feeder must be provided with a large number of elements. The structural complexity of the document feeder makes the production of the feeder a complex process.